Background Evidence suggests an association between some infections and key components of brain health: cognition, mental health, and sensorimotor function or frailty. The global burden of both infections and poor brain health is disproportionately high in low- and middle-income countries (LMICs). However, there is limited evidence on the relationship between infections and poor brain health from LMICs. Therefore, we investigated associations between nine infections and cognitive function, depression, and frailty in India.

Methods We conducted a cross-sectional study using data from Wave 1 (2017-2019) of the Longitudinal Aging Study in India (LASI) survey, a survey of adults (≥45years) from 35 of India’s 36 states and union territories. Survey data were collected via face-to-face interviews and direct health measurements. We investigated the association between nine self-reported infections (jaundice/hepatitis, malaria, tuberculosis, typhoid, chikungunya, diarrhoea/gastroenteritis, dengue, urinary tract infection [UTI], periodontal disease) during the two years before interview and global cognitive function, depression, and frailty. To account for selection probabilities and adjust for nonresponse, we survey-weighted logistic regression analyses to compare the odds of impaired cognition, depression, or frailty in people with at least one infection and each infection type compared to those without.

Results We included 64,881 respondents; median age 59 years (IQR:50-67), 53.5% female. Thirty-five percent of respondents reported having at least one of nine infections in the past two years. After controlling for demographic, social/environmental, lifestyle, and chronic health conditions, we saw evidence of an association between having at least one infection and both depression (OR: 1.24 [95%CI: 1.17-1.30]) and frailty (OR: 1.78 [95%CI: 1.69-1.87]). We saw particularly strong associations between: 1) periodontal disease and both depression (OR: 1.25 [95%CI: 1.17-1.33]) and frailty (OR: 1.96 [95%CI:1.84-2.08]); 2) chikungunya and depression (OR: 1.28 [95%CI: 1.10-1.49]) 3) UTIs and frailty (OR: 3.08 [95%CI: 2.65-3.59]); and 4) jaundice/hepatitis and frailty (OR: 2.20[95%CI: 1.90-2.54]). In contrast, having at least one infection was associated with reduced odds of impaired cognition (OR: 0.78 [95%CI: 0.73-0.84]).

Conclusion Our results suggest that infections are associated with increased depression and frailty in adults ≥45 years in India. However, we saw that reported infections were associated with better cognition, which may be explained by preferential recall of infections in those with better cognition. Longitudinal studies are needed to investigate a causal link between infections and adverse brain health, and guide interventions to reduce the burden of impaired cognition, depression, and frailty in India and LMICs more widely.